1. Field of the Invention
The invention relates to moving media technology and, more particularly to an improved mechanism for positioning a transducing head on a recording disk.
2. Description of the Prior Art
In the above-referenced copending U.S. patent application Ser. No. 386,862 of Charles Lindberg, et al. there is described a disk drive that generates a smooth spiral during the recording of data so that the recording operation is continuous. By superimposing onto the spiral-generating mechanism the capability of modifying the instantaneous head position, the recorded track is followed during playback. A magnetic read/write head is mounted so that it can move generally along a radius of a disk. A rotary motor is used to spin the disk and to drive a gear train. The output of the gear train is used to move the mounted head across the disk. The pitch of the spiral generated is controlled by the relative gear ratio between the disk and the head mechanism. Rapid retrace of the head mechanism to its starting position is accomplished by placing a return spring on the head mechanism and a clutch in the gear train. The apparatus will reliably generate a spiral over and over again. The operation of the clutch, however, scrambles the relationship between the disk and the head so that a second spiral is not likely to exactly coincide with an earlier spiral. Removing and reinserting the disk from the drive will also scramble the orientation of the spiral. Furthermore, two disk drives will not, due to manufacturing variations, generate the same pitch spiral. To resolve these problems, the connection from the gear train to the head mechanism is made variable, under the control of a second motor, so that the head can be made to follow the previously-recorded track. The track following can be done by dithering the head and using the demodulated head output as a steering signal, as described in the above-referenced patent application Ser. No. 371,862 of Armin Miller, et al. The mechanism does not, however, produce a means for moving the head rapidly across the disk to rapidly locate a particular track.
Presently-available disk drives do have mechanisms for spinning the disk and for rapidly moving the head across the face of the disk to rapidly locate a particular track. These two motions are usually accomplished with two motors since their basic characteristics are different. The disk is spun smoothly at a constant speed while the head is jerked violently from one track to another. Higher-performance disk drives are capable of high performance because the head actuator is quicker, and thus usually more powerful. In multidisk drives, where several disks are on a single spindle and where several heads are moved together, the resulting head-actuator mechanism is very bulky.
At the current state of the art, disk drives are becoming faster because of quicker head actuators, and they are also increasing their storage capacity. Improved magnetic materials and read/write heads contribute to this increased capacity by increasing the bits stored per linear inch of recorded track. Further improvements are being made by increasing the number of tracks per inch. As the number of tracks per inch has increased, the head actuator indexing mechanism for determining the exact location of a track has becomed more sophisticated. As the art has progressed, stepper motors driving cams have given way to DC motors, linear or rotary, controlled by linear incremental encoders, which are followed by servo control tracks on the magnetic surfaces themselves. The head actuator must be strong and powerful in order to jump quickly across a disk, and yet be able to precisely follow tracks which, as the state-of-the-art progresses, become finer and finer. Further, as the track densities become greater, the imperfections of the disk-spinning operation become more and more unavoidable, imperfections like bearing eccentricities, differential thermal expansion of the disk, vibrations in the mounting base, vibrations in the disk, etc. Thus, the head mechanism must also be capable of quick, fine adjustments in position in order to precisely follow the tracks. This requires a fine, light mechanism, a mechanism that is in contrast to the large, powerful mechanisms used in the past. This contrast in mechanism requirements has led to the present invention.
The primary object of this invention is to provide an improved mechanism for positioning a head on a disk, thereby achieving increased performance at lower cost.
A further object of this invention is to provide an improved mechanism for positioning a head on a disk which is less bulky than currently-available mechanisms.